Melt the butter in a medium saucepan. Add the onion and saute until soft and transparent.

Stir in the ketchup, water, Worcestershire sauce, brown sugar, vinegar, tomato paste, dry mustard and pepper. Stirring continuously, simmer uncovered for 15 minutes.

Remove from heat. Immediately stir the prawns into the sauce, covering them completely. Let them stand for 15 minutes.

Heat the grill and grease the rack. Remove the prawns from the sauce. Wrap each prawn in a piece of bacon and secure with a wooden pick, or thread 4 bacon-wrapped prawns onto a skewer. Place on the greased rack, on high heat, and cook for 3 to 4 minutes. Then turn them and cook the remaining side until the bacon is crisp.

Reheat the sauce and serve separately as a dipping sauce.

This recipe makes 6 main dish servings or 12 appetiser servings.